Conventionally, in an image forming apparatus, a cleaning blade is used to clean a transfer residual toner remaining on a surface of a rotating member, which is a photosensitive element, after an image transfer process (for example, Patent Documents 1 and 2). The cleaning blade is disposed to extend in a longitudinally parallel direction with respect to the rotating member and arranged so as to contact with the rotating member or to have a predetermined distance from the rotating member.
In recent years, high quality is strongly demanded for an image formed by electrophotographic image forming apparatuses. To improve the image quality, it is effective to decrease the size of toners and to form the toners in a spherical shape. A toner (hereinafter, “spherical toner”) having substantially a spherical shape formed by polymerization is becoming the mainstream. The spherical toner has higher transfer efficiency than a conventional powder toner (irregular-shaped toner), and is known to meet the recent demand for high image quality. However, the spherical toner increases Van der Waals force to the photosensitive element, thereby increasing adhesive force to the photosensitive element. Therefore, contact pressure of the conventional cleaning blade applied on the photosensitive element to clean the powder toner is not sufficient enough to scrape off the residual toner on the photosensitive element. By increasing contact pressure of the cleaning blade on the photosensitive element, the residual toner on the photosensitive element can be scraped off. However, when the contact pressure is too high, frictional force between the cleaning blade and the photosensitive element increases. Consequently, a front end of the cleaning blade is curled or vibrated, thereby generating a small gap between the cleaning blade and the photosensitive element. Since a polymer toner is very small, there is a possibility that the polymer toner passes by the cleaning blade even if the gap is very small. Accordingly, to prevent the curling of the front end and to satisfactorily scrape off the residual toner, the cleaning blade needs to be brought into contact with the photosensitive element in high precision, thereby obtaining an appropriate contact pressure.
Conventionally, the cleaning blade is installed in a cleaning case including a collecting unit that collects toner scraped off by the cleaning blade. This cleaning case is installed on a cover (a frame) that supports the photosensitive element, thereby positioning the cleaning blade on the photosensitive element (for example, Patent Document 3). At the time of positioning the cleaning blade on the photosensitive element by installing the cleaning case on the cover, it has been difficult to bring the cleaning blade into contact with the photosensitive element in high precision, due to an assembling error between the cleaning blade and the cleaning case and between the cleaning case and the frame.
The applicant of the present invention has developed a unit that directly mounts a cleaning blade on a frame that supports a photosensitive element, to increase the precision of bringing the cleaning blade into contact with the photosensitive element. FIG. 14 is a perspective view of relevant parts of the unit. As shown in FIG. 14, a frame 500 that supports a photosensitive element 2 has a positioning hole 503 for positioning the photosensitive element 2 within the frame, on a side plate 500a. A bearing 504 is engaged with this positioning hole 503. The frame 500 supports the photosensitive element 2, by inserting a rotation axis 2a of the photosensitive element into the bearing 504. The frame 500 has a blade contact surface 501 that extends from this side toward the back in FIG. 14 and to which a cleaning blade 11 is brought into contact. A boss 502 as a blade positioning unit that positions the cleaning blade 11 is provided on the contact surface 501. Since the cleaning blade 11 is brought into contact with the contact surface 501 of the frame 500, a contact angle with the photosensitive element 2 is kept at a predetermined angle. The cleaning blade 11 is positioned on the boss 502 provided on the frame 500 that supports the photosensitive element 2. The cleaning blade that is positioned by being directly fit to the frame that supports the photosensitive element is superior to the conventional cleaning blade that is positioned by being indirectly fit to the frame via the cleaning case in that there is no assembling error between the cleaning case and the cleaning blade. Therefore, the precision of bringing the cleaning blade 11 into contact with the photosensitive element 2 can be increased, as compared with the conventional method.
Patent Document 1: Japanese Patent Application Laid-open No. 2004-117696
Patent Document 2: Japanese Patent Application Laid-open No. 2004-177935
Patent Document 3: Japanese Patent Application Laid-open No. 2002-328583